The present invention relates to a fuel pressure regulator for use in an electronically controlled fuel injection device of an internal combustion engine and, particularly, to such a regulator capable of varying the pressure of fuel supplied to a fuel injection valve arbitrarily according to an operating condition of the engine.
A conventional fuel pressure regulator used in a fuel injection device of an internal combustion engine mounted on an automobile, etc. includes a valve member supported by a diaphram serving as a pressure receiving plane for fuel supplied under pressure by a pump, a valve seat associated therewith, a first chamber defined by the diaphram and mounting the valve member and the valve seat, and a spring having a predetermined mounting load mounted in a second chamber defined by the diaphram for biasing the valve member toward the valve seat. The second chamber is communicated to atomosphere or to a suction tube, so that, when the fuel pressure exceeds a preset value, the valve member is separated from the valve seat against the spring force and, otherwise, the valve member is urged to the valve seat to close a passage, resulting in a constant fuel pressure in the first chamber. The preset value is usually regulated to 2 to 3 Kg/cm.sup.2. Therefore, the mounting load of the spring is not less than 10 Kg since it is a product of the fuel pressure and the pressure receiving area of the diaphram.
Therefore, in order to vary the preset pressure value according to the operating condition of engine, it is necessary to change the mounting load of the spring, which is as large as 10 Kg, as proposed in, for example, Japanese Kokai No. 132068/1985. An electromagnetic device capable of directly performing such change is very large in size and so it is practically very difficult to employ such a proposition for a vehicle mounted device.